1. Field of the Invention
The present invention relates to electrostatographic machines such as copiers or printers, and more particularly to a development apparatus for use in such machines to develop latent images on an image-bearing member with toner particles.
2. Brief Description of the Prior Art
Electrostatographic process machines such as copiers and printers, which, for example, produce or reproduce toned images on selected substrates by employing electrostatic charges and toner particles on an dielectric image-bearing surface such as a photoconductive surface are well known. Typically, such machines operate through a sequence of currently well known steps. In a copier or printer type of such machines, for example, these steps include (1) charging of an insulated photoconductive surface with electrostatic charges, (2) forming a latent image electrostatically on such surface by selectively discharging areas on such surface, (3) developing the electrostatic image so formed with particles of toner, (4) transferring the toned image to a suitable substrate for fusing thereon to form a permanent record, and (5) cleaning by removing residual toner and/or other particles from the photoconductive surface in preparation for similarly reusing the surface to produce another such image.
The images so produced can be in the form of line copy, half-tones, or solid colors, for example, solid blacks when black color toner particles are used in the development step. Line copy images so produced include magnetic characters for processing on magnetic ink character recognition or (MICR) equipment. The effectiveness and reliability of such MICR equipment, as well as a significant degree of the overall quality of the toned characters produced by the electrostatographic machine, depend importantly on the efficiency and quality of the development step. Several types of development apparatus therefore have been developed and continue to be developed for performing such efficient and quality image development as required.
Some examples of such development apparatus are disclosed in U.S. Pat. No. 3,543,720, issued Dec. 1, 1976 in the name of Roger A. Drexler and illustrated in FIGS. 2, 3, and 4 of the drawings to this application. As disclosed in FIGS. 2-4, such a development apparatus shown generally as 130, includes an elongate housing 42 and two development rollers 44, 46. The housing 42 has a first sump portion 48 within which is located a feed auger 50 for mixing and feeding developer material 131 from the front end 52 of the apparatus 130 to the rear end 54 thereof. Developer material 131 or fresh toner particles added into a front portion 56 of the apparatus 130 (FIG. 1) is moved by the feed auger 50 from the front end 52 to the rear end 54.
Ordinarily, the developer material 131 consists of non-magnetic toner particles and of magnetizable iron carrier particles. As shown in the drawings of FIGS. 2-4, the development rollers 44 and 46 are each provided with sets of magnets for example, the sets SIN1, and S2N2-N5S3 of roller 46, which have polarities as shown. The magnets are mounted therewithin for magnetically attracting the developer material 131 onto the surface of each roller 44, 46. As shown, each roller 44, 46 includes a non-magnetic rotatable outer shell 60, 62 respectively and a stationary core 64, 66 respectively onto which the sets of magnets are assembled. Magnetic fields generated by each set of magnets attract the developer material 131 and hold it on the surface of the shell 60, 62 respectively, while such shell 60, 62 is being rotated in the direction of the arrows 68, 70 for example. As is well known, as the shells 60, 62 are being rotated, as such, through areas with, and areas without magnetic fields (FIGS. 3 and 4) about each roller 44, 46, the magnetized developer material 131 on each roller will form bristle-like patterns which stand up within the magnetic field areas. These bristle-like patterns, however, will collapse into a loose non-magnetic pile in non-magnetic field areas, for example in the area shown as 72 (FIG. 3).
As shown in FIG. 2, as the feed auger 50 moves the developer material 31 from the front end 52 to the rear end 54, the development rollers 44, 46 also move such developer material around from side-to-side and up-and-down within the housing 42. In an electrostatographic copier or printer, the rollers 44, 46 can thus move the developer material 31 into development contact with electrostatically formed images 74 being carried on an adjacently mounted image-bearing member 76 moving, for example, in the direction of the arrow 78. Development of the images 74 through such contact of course uses up or depletes toner particles contained in the developer material 131.
Accordingly, as shown in FIGS. 2 and 3, the apparatus 130 includes means shown generally as 80 for moving spent or toner depleted developer material from the rear end 54 back to the front end 52, and for for balancing the end-to-end flow of the developer material 131 therewithin. The means 80 includes a second sump portion 82 within which is located a return auger 84 for moving the spent developer material from the rear end 54 back to the front end 52. Means such as a paddle wheel 85 located within the front portion 56 then move the spent developer material from the second sump portion 82 back over to the first sump portion 48. Fresh replenishment toner particles can then be added appropriately into the spent developer material as it is being moved as such through the front portion 56.
The means 80 also includes an opening 86, which is formed through a sump dividing wall, into the sump 82, and a mechanical skive plate 88 which is mounted within the opening 86 and projects into a small gap forming relationship with the periphery of shell 62 of development roller 46. As shown in FIGS. 2-4, the plate 88 is mounted such that its skiving edge 90 forms such a small gap against the roller 46 in the non-magnetic field area 72 of roller 46. As shown in FIG. 2, the desirability and need to form such a gap in a non-magnetic field area are so important that one of the magnets adjacent thereto, shown as a south pole magnet S3 is shortened so as to leave a non-magnetic field area within the gap. Note that ordinary type developer material 131, which contains magnetizable carrier particles and non-magnetic toner particles, collapses into a loose non-magnetic pile on the surface of the roller 46 when being moved through such a non-magnetic field area 72. As such, there are no undesirable forces to interfere with the plate 88 easily and effectively skiving off or removing a predetermined partial amount of such a loose non-magnetic pile of the developer material 131 from the development roller 46. The partial amount so removed drops gravitationally into the sump 82 and can then be returned by the auger 84, from the rear end 54 to the front end 52.
Unfortunately, however, the apparatus 130 of FIGS. 2-4, and particularly its partial skiving features shown as 80 have been found not to work well, for example, with magnetic developer material containing magnetic particles. An example of such magnetic developer material is disclosed in commonly assigned U.S. patent application Ser. No. 433,248, filed Nov. 8, 1989 in the names of John M. Spence, Robert E. Contois, and Lawrence P. DeMejo, and entitled "TWO-COMPONENT MAGNETIC DEVELOPER FOR MAGNETIC CHARACTER RECOGNITION." The contents of this particular U.S. application are hereby incorporated by reference.
As disclosed in this incorporated U.S. application, the magnetic developer material therein consists of needle- or acicular-shaped magnetic stainless steel carrier particles, and of magnetic toner particles. The magnetic toner particles include particles of a binder resin medium, and particles of magnetic material dispersed therein. The magnetic developer material, as such, possesses magnetic fields of its own which result in the formation of magnetic chains of the particles thereof.
In the prior art apparatus 130 of FIGS. 2-4 for example, when magnetic developer material such as that disclosed in the incorporated application is moved around therein by the development rollers 44, 46, such magnetic chains will stand up in the form of bristles when moving through the magnetic field areas of each roller. Unlike the case of ordinary developer material 131 however, these magnetic chains of the magnetic developer material continue to persist even in the non-magnetic field areas of such rollers, for example the area 72 of the roller 46. Unfortunately, in the non-magnetic field area such as 72 where the partial skiving means 80 are located, these persistent magnetic chains span the small gap between the roller 46 and the edge 90 of the plate 88, thereby bridging and closing off the gap. As a result, attempts to partially remove some of the magnetic developer material D fail and all of such magnetic developer material which contacts the skiving edge 90 is skived off or removed by the plate 88 from the roller 46, and is directed into the sump portion 82 for return to the front end 52. Attempts to remedy this by widening the gap thereat, results instead in the persistent magnetic chains causing all such magnetic developer material thereat to slide through the widened gap and under the edge 90 of the plate 88 despite making what would otherwise be a partial skiving contact with the skiving edge 90.
Such all-or-nothing flow of the magnetic developer material over or under the plate 88, of course, results in an unbalanced flow of such developer material in the apparatus 130, and more importantly, in poor image development by the electrostatographic apparatus or machine 10.